Deltadromeus

Deltadromeus (meaning "river delta or change runner") is an extinct genus of controversial theropod dinosaur that lived in present-day Morocco during the mid-Cretaceous period. It was described by American paleontologist Paul Sereno and colleagues in 1996. The genus contains a single species, D. agilis, named based on an incomplete postcranial skeleton, the holotype specimen. However, some fossils from the Bahariya Formation of Egypt that were formerly referred to the theropod Bahariasaurus have been suggested to belong to Deltadromeus. The holotype specimen of Deltadromeus was unearthed by a joint expedition by the University of Chicago and the Service Géologique du Maroc in Errachidia Province, eastern Morocco in rock layers coming from the Gara Sbaa Formation of the Kem Kem Beds. This indicates that these fossils date to the Cenomanian stage of the Cretaceous period, 100-95 million years ago.

Deltadromeus was around 8 metres (26 ft) in length and 1,050 kilograms (2,310 lb) in weight based on the holotype. If the Egyptian remains do belong to Deltadromeus, this would make it among the longest known theropod genera at around 12.2 metres (40 ft), comparable to Tyrannosaurus. The forelimbs of Deltadromeus are relatively long for a theropod, being proportionately longer than those of taxa like Allosaurus. Deltadromeus also preserves gracile, slender, and relatively long hindlimbs, indicating it was cursorial. Its tail vertebrae have broad, quadrangular neural spines (spines emerging from the base of the vertebra) with pleurocoels (cavities) which would store pneumatic air sacs.

The classification of Deltadromeus has been in flux since its original description. Originally Deltadromeus was considered to be a basal coelurosaur related to Ornitholestes; however, later studies have challenged this idea. Some studies have classified it as an avetheropod closely related to Gualicho or as a megaraptoran outside the family Megaraptoridae. Other studies have proposed that Deltadromeus is a ceratosaur; however, its position within Ceratosauria is debated. Studies have classified it as a basal ceratosaur, noasaurid, or an Elaphrosaurus-grade ceratosaur. Many studies find that it is a ceratosaur of some kind, supported by several phylogenetic analyses. Additionally, some studies have suggested that it may be a junior synonym of Bahariasaurus, another potential ceratosaur which lived around the same time and region as Deltadromeus.

Many gigantic theropods are known from North Africa during this period, including Deltadromeus and Bahariasaurus as well as the spinosaurid Spinosaurus, the carcharodontosaurids Carcharodontosaurus and Tameryraptor, and several unnamed abelisaurids. If Deltadromeus is a ceratosaur closely related to the herbivorous/omnivorous Limusaurus and Berthasaura, it possibly would be herbivorous or omnivorous. This would indicate more niche partitioning in theropods in Cretaceous North Africa and suggest that Deltadromeus filled a role traditionally filled by ornithischians. North Africa at the time was blanketed in mangrove forests and wetlands, creating a hotspot of fish, crocodyliforms, and pterosaur diversity.